SlideRocket is an online service which allows you to create beautiful presentations online. This is a great alternative to Powerpoint and other online web applications that provides a similar service. SlideRocket will give you a 250MB of free storage and limited/basic online editor functionality.
SlideRocket has all the features of popular presentation applications plus a few unique ones of its own. Like in Google Docs, the presentations made using SlideRocket can easily be shared. It can be easily emailed to anyone or embedded on websites. Speaking of Google Docs, you can also integrate them to your SlideRocket presentations. This is also true for Powerpoint presentations.
If ever you are in need of an alternative to popular presentation tools, particularly one that you can use online, SlideRocket is definitely worth a checkout. Below is a sample presentation of SlideRocket.
You might also want to try FlowGram